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Bra Size Calculator

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Enter your band (underbust) and bust measurements to find your bra size.

Bra Size Calculator

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US size
30D
UK size
30D
EU size
65D
Sizing conventions vary by brand and country - use this as a starting point, and always check a specific brand's own size chart when possible.

The method

Band size = underbust measurement, rounded to the nearest even number Cup size = (bust measurement - band measurement), each inch of difference = one cup size letter
Example

30 inch band, 34 inch bust: difference = 4 inches = D cup, giving a US/UK size of 30D.

Step-by-step guide

  1. Measure your band - wrap a tape measure snugly around your ribcage, directly under the bust.
  2. Measure your bust - wrap the tape around the fullest part of your bust, keeping it level.
  3. Read your size in US, UK, and EU conventions.

Why US and UK sizes look the same but EU sizes look different

US and UK band sizes are both measured in inches and use the same letter-based cup system, which is why they typically match. EU (and most of continental Europe's) sizing instead measures the band in centimeters and shifts the numbering scale accordingly - a US/UK 30 band converts to roughly a EU 65, following a fairly consistent offset. Because the underlying measurement and conversion are standardized this way, the cup letter itself usually stays the same across US, UK, and EU sizing, even though the band number changes.

Common mistakes

Measuring the band too loosely - it should be snug (you should be able to fit one or two fingers under it, no more), not the same looseness as a casual measurement.
Assuming cup size is an absolute measurement - a D cup on a 28 band is a much smaller physical cup volume than a D cup on a 38 band, since cup size is always relative to the band underneath it.

Frequently asked questions

Why do sizes vary so much between brands?

Bra sizing isn't as tightly standardized across manufacturers as something like shoe sizing - cut, wire shape, and fabric all affect fit, so the same calculated size can fit differently between brands. Use this calculation as a starting point for which size to try first.

What if my calculated cup size seems off compared to what I usually wear?

This is common and usually comes down to two things: measurement technique (band tightness matters a lot) or genuine differences between brands' size charts. If your current bra fits well, that fit is a more reliable guide than any single calculation.

Does this work the same for all cup sizes?

The basic one-inch-per-cup-size logic is the standard convention, though some brands' internal sizing deviates at larger cup sizes. This calculator covers the common range from AA through J.

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